Vines grow strong on carbon dioxide diet

WASHINGTON – Vines – poison ivy, Japanese honeysuckle, kudzu – snake through the backyard, girdling trees and strangling shrubs, thriving, scientists say, on the same pollution they blame for global warming.

From backyard gardens to the Amazon rain forest, vines are growing faster, stronger and, in the case of poison ivy, more poisonous on the heavy doses of carbon dioxide that come from burning such fossil fuels as gasoline and coal.

Complaints about vine infestation have increased tenfold in a decade, said Carole Bergmann, forest ecologist for the Maryland-National Capital Parks and Planning Commission, which serves Montgomery and Prince George’s counties in Maryland. Vines have choked gardens, ruined brickwork, disrupted bird habitat, and clogged paths, ponds and air conditioning and electronic equipment.

“The woods they used to know have just changed character,” Bergmann said. “They’re covered with vines. The trees are being weakened and falling over – or strangled.”

That leaves scientists worried that the forest of the future could become a weedy tangle of hyper-vines choking off the trees, which absorb more carbon dioxide.

As vines become stronger, they also grow more various, a problem researchers say is at least partly attributable to climate change.

“Fifteen years ago, kudzu” – known as the vine that ate the South – “would not survive in the D.C. area,” Bergmann said, because the climate was too cold. “Now it survives even up in New York.”

For six years, Jacqueline Mohan has worked at Duke University to study elevated carbon dioxide levels’ effect on woodland life.

Pumping carbon dioxide through pipes into a North Carolina pine forest, Mohan found that poison ivy grew at 2 1/2 times its normal rate, an increase five times the average gain for trees. The noxious vine grew thicker, used water more efficiently and became far more allergenic to humans.

“Poison ivy is fascinating with its medical implications. But what’s really important scientifically is these woody vines have been increasing in abundance all over the planet (and) inhibiting the growth and regeneration of the forest,” said Mohan, who released her findings last month.

“This work suggests that atmospheric carbon dioxide is at least partially responsible.”

But the vines also hint at a tantalizing solution to global warming: Perhaps scientists can engineer a plant that would absorb extraordinary amounts of carbon dioxide and clean the air without throwing forests wildly off kilter.

“There’s some reason for optimism that we could use vegetation to stave off global warming,” said William Schlesinger, an expert on climate change and dean of the Nicholas School of the Environment and Earth Sciences at Duke University. “But there’s no telling that the mix you come to is going to be stable or functional the way today’s ecosystems are.”

Trees and plants play a vital role in soaking up carbon dioxide that is released into the atmosphere. Scientists are trying to determine whether plants can keep pace with – or perhaps even begin to reverse – the rise in carbon dioxide.

For 20 years, Bert Drake has been exposing marsh grasses to twice as much carbon dioxide as normally found in the atmosphere. On a recent day, he strolled the wooden decking that winds through his laboratory, a swath of Chesapeake Bay marsh at the Smithsonian Environmental Research Center in Edgewater, Md.

Drake said his research suggests that most plants grow faster on higher levels of carbon dioxide – including plants already used as alternative fuels, such as switch grass. If burned instead of fossil fuels, these plants, the theory goes, could form a defense against climate change.

But whether every plant will grow faster in those conditions, or how fast, or at all, is maddeningly unpredictable.

At Edgewater, Drake found that most grasses grow about 35 percent faster in the altered atmosphere. But they are able to grow much faster than that, a variance he can’t fully explain. Similarly, his experiments on oak trees in Florida found that each oak species responds differently to the same carbon dioxide overload.

“It’s quite imaginable that we could make an oak tree (that is) more efficient at trapping carbon dioxide for us,” Drake said. “But until we know a lot more about how each species responds, we can’t make solid predictions.”